The discovery of single-molecule and single-nanoparticle surface-enhanced Raman scattering (SERS) has attracted considerable interest, both for fundamental studies of enhancement mechanisms and for potential applications in ultra sensitive optical detection and spectroscopy. A number of researchers have shown that the enhancement factors are as large as 1014-1015, leading to Raman scattering cross sections that are comparable to or even larger than those of fluorescent organic dyes. This enormous enhancement allows spectroscopic detection and identification of single molecules located on the surface of single nanoparticles or at the junction of two particles at room temperature. Progress has been made concerning both the structural and mechanistic aspects of single-molecule SERS, but it is still unclear how this large enhancement effect might be exploited for applications in analytical chemistry, molecular biology, or medical diagnostics. One major problem is the intrinsic interfacial nature of SERS, which requires the molecules to adsorb on roughened metal surfaces. For biological molecules such as peptides, proteins, and nucleic acids, surface-enhanced Raman data are especially difficult to obtain, hard to interpret, and nearly impossible to reproduce. Therefore, a need in the industry exists to improve SERS data for biological molecules.
Various bacteria are responsible for numerous human diseases. For example, Escherichia coli can cause several intestinal and extra-intestinal infections such as urinary tract infections, meningitis, peritonitis, mastitis, septicemia, and Gram-negative pneumonia. Bacterial infections, such as these noted above, are the cause of millions of hospitalizations and thousands of deaths each year. Current detection and diagnostic methods for many bacterial pathogens are not sensitive enough for early and rapid detection. Thus, improved systems and methods for the detection of pathogens and other biomolecules are needed.